Questions and Answers
Which of the following best defines life history?
What characterizes the growth and reproduction patterns of elasmobranchs?
Energy can be created and destroyed according to life history trade-offs.
False
What happens to the lifespan of an organism if it grows rapidly?
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Elasmobranchs have ______ fecundity and high survival rates.
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Match the life history traits with their corresponding impacts:
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Which of the following is NOT a key aspect of somatic growth in fisheries?
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Somatic growth is solely concerned with reproduction in fisheries.
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What is a primary characteristic of somatic growth that is important for fisheries?
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Somatic growth allows for the approximation of other important life history parameters such as maximum _____.
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Which length measurement represents the distance from the tip of the snout to the end of the caudal fin?
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The measurement of skates and rays is primarily determined by their disk ______.
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Match the following measurements with their definitions:
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Which length type represents the distance from the tip of the snout to the end of the caudal fin?
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The second dorsal fin is typically used for age determination because it is often more worn than other fins.
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What is the significance of growth bands in spines?
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What is a primary benefit of the bomb radiocarbon method for age validation?
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The delta14C value can determine the exact age of a sample.
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What is the primary purpose of the Mark-Recapture method with chemically tagged wild fish?
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The major disadvantage of the Mark-Recapture method is that it provides a strong validation of growth band formation.
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What kind of chemicals are commonly used for tagging fish in the Mark-Recapture method?
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What is a limitation of using vertebrae to determine the age of some shark species?
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Mark-recapture tagging methods are always unbiased and provide accurate growth estimates.
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What curve can be used to estimate age from length data in shark populations?
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What is the average gestation time for sharks?
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Shark offspring receive extensive parental care after birth.
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What is the term used to describe the interval between successive births of the same female shark?
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Fecundity refers to the ______ size in sharks.
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Match the following terms related to shark reproduction with their descriptions:
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What is the maximum age on record for a species often referred to as?
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Predation is a form of natural causes that contribute to fish mortality.
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What is the formula that relates longevity in years to the rate 'k'?
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What does life history trade-off primarily involve?
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Energy allocation in life history trade-offs can result in unlimited growth potential.
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What is the principle that energy cannot be created nor destroyed known as?
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Study Notes
Life History Trade Offs
- Energy from foraging is utilized for various physiological processes: body growth, metabolism, excretion, and reproduction.
- Energy is a limited resource; it cannot be created or destroyed, leading to trade-offs in energy allocation.
- Rapid growth can lead to increased mortality; energy invested in growth reduces lifespan.
- Organisms that grow quickly tend to mature faster but have shorter overall life spans.
- Shorter life spans often correlate with earlier reproductive strategies; organisms may reproduce sooner if their lifespans are limited.
Characteristics of Elasmobranchs
- Elasmobranchs, including sharks and rays, exhibit distinct life history traits:
- They tend to grow into large adults and produce large pups.
- They demonstrate low fecundity, meaning they have fewer offspring.
- These species generally have high survival rates despite slower growth rates.
- They reach sexual maturity later in life and tend to have longer lifespans compared to many other fish species.
Growth in Fisheries
- Individual growth refers to increases in body mass and length of fish.
- Somatic growth is crucial in fisheries management for several reasons.
Importance of Somatic Growth
- Determines biomass gain for fish stocks, impacting sustainability and resource management.
- Influences key life history characteristics like maturation, affecting breeding and population dynamics.
- Enables the estimation of other important life history parameters, such as maximum age of fish.
- Establishes a relationship between length and age, aiding in age determination for stock assessments.
Measuring Sharks
- Length serves as a reliable estimate for weight, and weight can also be inferred from length.
- Length is typically recorded along the shark's curved body and presented in centimeters (cm).
- Weight is commonly reported in grams (g).
- Total length is defined as the measurement from the tip of the snout to the end of the caudal fin.
- Precaudal length is measured from the tip of the snout to the caudal precaudal pit, which is important for certain assessments.
- Fork length is taken from the tip of the snout to the midpoint of the fork in the caudal fin, crucial for specific species identification.
Measuring Skates and Rays
- The primary measurement for skates and rays is disk width, a crucial metric for understanding their size and biology.
Length Types
- Three main length measurements are utilized: fork length (FL), precaudal length (PL), and total length (TL).
Spines and Age Determination
- Spines exhibit distinct growth bands, useful for age estimation.
- Growth bands have been confirmed to form annually in certain species, like the Spiny Dogfish (Squalus acanthias).
- The second dorsal fin is preferred for age determination due to its lesser wear compared to other fins.
- Fin spines can be challenging to analyze: they are often too large for dissection microscopy and too faint or narrow for visual counting.
- Digital imaging is recommended for spines: capture images using a standard digital camera setup, then enhance for clarity before determining age.
- Adequate lighting is crucial for successful image capture and subsequent age determination.
Release of Known Age and Marked Fish Into Wild
- Utilizes fish marked with tags or chemically through calcium binding compounds for tracking.
- This method is the most rigorous for age determination but is ineffective for long-lived species.
Bomb Radiocarbon
- Derived from the radiocarbon produced during nuclear bomb testing.
- Serves as an exceptional age validation technique for long-lived elasmobranchs (e.g., sharks and rays).
- Functions as a large-scale chemical tagging experiment, providing a unique age estimation method.
- Delta14C values establish a minimum age for samples, with 1958-1965 being the most critical period for accurate Delta14C aging.
- The low decay rate of 14C allows for both archived and currently collected samples to be used for testing.
- Costs range from 500to500 to 500to1000 per sample, with a relatively small number of samples needed for effective age validation.
Mark-Recapture Method for Fish Growth Validation
- Effective for validating growth band formation in elasmobranchs.
- Utilizes calcium-binding chemicals like oxytetracycline, alizarin, calcein, or strontium for tagging fish.
- Chemicals are injected at tagging and are absorbed into fish vertebrae and spines, creating a permanent mark.
- Marks are visible under fluorescent light and indicate the growth band formed during tagging.
Advantages and Disadvantages
- Advantage: Validates growth bands while fish grow in their natural habitat, leading to accurate growth estimations.
- Disadvantage: Low number of increments formed post-tagging may lead to significant relative error if increments are misinterpreted.
Best Practices for Robust Validation
- Tagging young fish and recapturing them at an older age yields the most reliable data on growth validation.
Application and Effectiveness
- Considered a powerful validation method alongside bomb radiocarbon dating for adult wild elasmobranchs.
Somatic Growth in Sharks
- Age determination in some shark species can be complicated by irregular vertebral formation, decay, or lack of annual growth bands, leading to potential mismanagement.
- Alternative methods such as mark-recapture tagging provide insights, yet they are limited by biases like growth variability among individuals, short library time, small sample sizes, or presence of outliers.
- Von Bertalanffy growth curves are utilized to estimate age based on length data, reflecting the average growth rate of shark populations.
- Growth rate is not uniform; it decreases as the length of the shark increases.
- Elasmobranchs, which include sharks, continue to grow throughout their entire lives, exhibiting indeterminate growth.
- Accurate age determination of elasmobranchs is particularly challenging, and errors in age assessment can lead to biased growth curves.
Reproduction in Sharks
- Life history theory suggests optimal paternal investment enhances offspring survival and future reproductive success.
- Maternal survival and reproductive potential balance against the level of paternal care provided.
- Sharks exhibit minimal parental care, relying on an enlarged liver and yolk sac for nourishment, with optimal pupping conditions.
- Shark offspring are independent at birth, exhibiting relatively large size and high survival rates.
- Gestation periods for sharks range from 6 to 36 months, with an average of 12 months.
- The reproductive cycle, or inter-birth interval, typically spans 1-3 years for female sharks.
- Litter sizes vary dramatically from 1 to 300 pups, with an average of 13 pups per litter.
- Data on size and age at maturity are often presented as the lengths and ages when 50% of individuals reach maturity, analyzed through logistic regression.
- A positive correlation exists between maternal size and both the size and number of offspring produced, indicating increased fecundity with larger females.
- Experience (related to food availability) and age (size) of the female are significant factors influencing reproductive outcomes.
- Certain shark species may experience a trade-off between increasing litter size and the mass of individual offspring.
- Understanding these reproductive traits is crucial for conservation and management strategies in shark populations.
- Fecundity shows a direct increase with maternal length, impacting population dynamics and sustainability.
Longevity in Species
- Longevity refers to the maximum age recorded for different species, providing insight into their lifespan potential.
- It indicates the maximum time available for an organism's growth and reproduction, influencing population dynamics.
- Longevity serves as an effective proxy for assessing natural mortality rates within species populations.
- Mathematical approximation of longevity indicates that it correlates to approximately 4.6 years per k (where k represents growth rate).
Causes of Natural Mortality
- Natural mortality encompasses various factors that lead to fish deaths, including:
- Predation: Other species consuming them as food.
- Disease: Illnesses that can lead to mortality among fish populations.
- Parasites: Organisms that live on or in the fish, potentially causing harm or death.
- Accidents: Unintentional events leading to death, such as getting caught in debris.
- Natural Death: General aging processes leading to mortality.
- Old Age: The eventual decline in health and vitality associated with aging.
Life History Trade Offs
- Foraging provides energy that is allocated to various biological functions including growth, metabolism, excretion, and reproduction.
- Energy allocation is crucial as it cannot be created or destroyed, leading to inherent trade-offs in life history strategies.
- Resources obtained through foraging must be carefully distributed among different life processes to maximize survival and reproductive success.
- The balance between somatic growth (body size and strength) and reproductive output is a key consideration in life history strategies.
- Trade-offs may result in prioritizing growth over reproduction or vice versa, depending on environmental conditions and species-specific life strategies.
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Explore the essential features of life history and how they relate to survival and reproduction strategies in organisms. This quiz will help deepen your understanding of the different stages that living beings go through in their life cycles.
